Biodiesel is a petroleum diesel fuel equivalent that can be produced from a variety of biological sources including vegetable oils and animal fats. Because biodiesel's combustion profile is similar to that of petroleum diesel, it can be used in conventional diesel engines either alone or blended with traditional petroleum diesel. Given that biodiesel is a renewable fuel source with a significantly reduced environmental impact, it is extremely attractive as a replacement or adjunct to traditional petroleum diesel.
Unlike traditional petroleum diesel, biodiesel can be produced from entirely renewable sources: vegetable oils and animal fats. Consequently, biodiesel is a renewable energy alternative to petroleum diesel that is increasingly seen as a natural resource with a finite, limited supply. Moreover, even if biodiesel is not used as a complete replacement for conventional petroleum diesel, it may at least supplement or augment conventionally sourced petroleum diesel, stretching out those limited supplies.
Biodiesel is also attractive when compared to traditional petroleum diesel because of its significant environmental benefits. First, biodiesel is an essentially carbon neutral fuel. Unlike petroleum diesel which releases carbon that was previously stored or captured underground upon combustion, virtually all of the carbon that makes up biodiesel originates in the atmosphere and is simply returned to the atmosphere upon combustion. Second, biodiesel has a significantly improved emissions profile relative to conventional diesel. Carbon monoxide, particulate matter, sulfates, polycyclic aromatic hydrocarbons and unburned hydrocarbon emissions are all reduced by over 50% in biodiesel when compared to conventional diesel. Many studies do indicate, however, that nitrogen oxide emissions may be slightly increased in biodiesel.
Biodiesel can be produced from the fatty acid triglycerides present in vegetable oils and animal fats. The triglycerides are converted into mono alkyl esters of long chain fatty acids, such as fatty acid methyl esters and fatty acid ethyl esters.
There are three basic methods for the production of alkyl esters from vegetable oils and animal fats. The most prevalent method is base catalyzed transesterification with alcohol. The two other methods include conversion of triglycerides into alkyl esters using enzymes like lipase, and the use of solid catalysts like calcium aluminate and zinc aluminate. Advantages of the base catalyzed reaction include relatively low processing temperature and pressure; high conversion in a minimal time; direct, single step conversion to methyl ester with no intermediate reactions; and a relatively simple reaction apparatus.
Given the relative ease of production of biodiesel, along with its renewable and environmentally friendly characteristics, biodiesel is a very attractive alternative energy source, and worldwide production of biodiesel has increased dramatically in recent years. In the United States, for example, production of biodiesel increased over ten fold from approximately 20 million gallons to 250 million gallons in the three year period from 2003 to 2006. These significant increases in production have resulted in an increased demand for biodiesel feedstocks worldwide.
Feedstocks for biodiesel include virtually any vegetable oil or animal fat. Soybean oil is the primary biodiesel feedstock, currently accounting for some 90% of biodiesel production worldwide. Other vegetable oils, such as corn, cottonseed, canola or rape seed, flax, sunflower and peanut, also are used, but these seed oils are generally more expensive than soybean oil. Moreover, the use of such edible oils for the production of fuel competes with their historical use in the food supply, raising concerns over future supply and costs as biodiesel feedstock demand continues to increase.
Because the use of edible oils as biodiesel feedstocks competes with their human consumption, other non-edible oil sources are particularly attractive for potential use as biodiesel feedstocks. Various types of non-edible oil bearing trees like Jatropha curcas are being cultivated in large scale for use as biodiesel feedstock. It is imperative, therefore, to develop a processing scheme that extracts the maximum amount of biodiesel from such non-edible sources.
Animal-derived products such as tallow, choice white grease or lard, poultry fat and yellow grease also contain triglycerides and are used as feedstocks. These products, when compared to plant-derived oils, often offer an economical advantage as a feedstock. There is also some preliminary indication that biodiesel from these sources, which are high in saturated fats, produces less nitrous oxide than biodiesel produced from plant oils.
The third main source of triglycerides is recycled oil and grease that can be obtained from restaurants and food processing plants. Although these recycled oils require more pre-treatment than is required for virgin vegetable oils, the use of a recycled product such as used cooking oil solves waste disposal problems and is economically attractive.
Although a number of approaches have been, and continue to be experimented with, the industry has still not been very successful in developing an economically viable biodiesel fuel which also meets the necessary quality standards.
WO 2006/043281 describes a process of chemical neutralization of seed oil, including from Jatropha curcas, and sending the by-product for soap making. It is well known that there is considerable loss both in terms of fatty acid and oil carry over by this method, thus limiting the yield and increasing the processing cost of oil. Also the oil expelling technique used in this method is energy intensive and leaves behind over 8% of the otherwise available oil in the seed cake. These less efficient approaches result in increased biodiesel production costs.
WO 2006/016492 describes a process of degumming and transesterification of oil to produce biodiesel. The disadvantage of carrying forward a simple degummed oil is that it allows heavy metals and other finely suspended matter in the final product, which may require high levels of stabilizers to preserve oxidation stability.
U.S. Pat. No. 6,399,800 suggests esterification of a dried, saponified feedstock as a process to convert fatty acids into fatty acid alkyl esters. This involves capital intensive special reactors, and requires a complex process to eliminate moisture from the saponified feedstock.
High levels of free fatty acids, which are often present in crude, old, or reused oils, can inhibit the catalysts used in conventional transesterification reactions. U.S. Pat. Publication No. 20050080279 provides a different way of handling oil with high free fatty acid content. The disclosure requires large amounts of glycerin to be used in the process, which requires equipment with greater capacity, and the disclosure also involves a more energy intensive process to obtain the correct yield.
U.S. Pat. Nos. 7,087,771 and 6,822,105 primarily address only the soap stock produced as a transesterification by-product, and do not explain forward or backward integration with all of the steps of the process from seed to biodiesel.
U.S. Pat. No. 6,013,817 describes a process wherein both the oil and free fatty acids are transesterified, resulting in not only greater throughput, but also greater catalyst consumption. Further, the process also requires reprocessing the soap stock formed of entire fatty acids back to glycerides. This again requires a time-consuming and lengthy process, larger equipment and greater processing costs due to multiple processing of same material.
U.S. Pat. No. 6,979,426 provides a modular biodiesel production unit with all of the necessary components incorporated onto one platform for ease of relocation. The modular production unit includes a mixing unit, a reactor unit, a separation unit, a distillation unit, and a filtering unit, all incorporated onto or into a self-contained platform or housing that is able to be easily relocated. This system does not, however, allow for fatty acid/soap stock recycling which is able to increase the yield of biodiesel.
PCT application WO 1999/026913 relates to a method and equipment for producing biodiesel economically in large-scale industrial equipment. However, this patent application does not deal with an integrated plant or process beginning with oil bearing seeds as a feedstock.
PCT application WO 2003/022961 relates to machinery for biodiesel production wherein specialized reaction tanks with vertical rotating feed tubes having separators, and inlet and outlet openings are used. The machinery occupies minimal plant space; minimal on-site feedstock; and minimal on-site storage. Again, there is no integration of seed processing to this system, resulting in lower overall yield of biodiesel from a given amount of seed.
U.S. Pat. Publication No. 20060260184 includes a method and apparatus for the production of biodiesel fuel, which includes a compact processor including a vapor recovery system for removing excess alcohols from the fuel and an additional chemical cleaner. However the publication does not address the recycling of by-products and waste to increase biodiesel yield.
Recently, ultrasonic reactors have been employed to dramatically speed up the transesterification reaction time. These reactors also have reduced amounts of catalysts required for the reaction, and result in better separation of the phases. Nonetheless, this ultrasonic approach is still relatively expensive.
Thus, there is a need in the art to be able to efficiently and inexpensively produce biodiesel from a variety of feedstocks including, in particular, inedible seed oils. Additionally, further processing of the by-products and intermediates of the production process itself, like the seed cake, crude oil, acid oil, spent bleaching earth, and soap stock, may also lead to the recovery of additional oil for transesterification. Finally, there is also a need for modular equipment for all of these processes which can be easily scaled up for large scale production of biodiesel.